1. Field of the Invention
The present invention relates to an intake system for a vehicle internal combustion engine that has multiple air intake ducts.
2. Description of the Related Art
Generally, in an intake system for a vehicle internal combustion engine (hereinafter, simply referred to as “engine”) that is mounted on a vehicle such as an automobile, air inhaled through an air intake duct is filtered by an air cleaner element in an air cleaner box and is supplied to an intake port of the engine. Further, multiple ducts may be provided to compensate for the lack of inhaled air when the engine operates at a high-speed high-load region.
Japanese Patent Application Publication No. 2002-195116 (JP-A-2002-195116) describes an intake system for the vehicle internal combustion engine in which a bifurcated air intake duct is connected to an air cleaner housing. When the engine operates at a low-speed low-load region, air is inhaled through only one of the openings of the intake duct. When the engine operates at a high-speed high-load region, air is inhaled through both the openings of the intake duct.
Further, Japanese Patent Application Publication No. 2000-303925 (JP-A-2000-303925) describes an intake system for the vehicle internal combustion engine that has two air intake ducts having resonant frequencies different from each other. One of the two intake ducts opens in a cowl box and the other opens to a fender. A desirable air intake sound is generated by inhaling air through these two air intake ducts when the engine operates at a high-speed high-load region, thereby realizing a powerful sporty sound.
However, the intake system for the vehicle internal combustion engine described in the above JP-A-2002-195116 or JP-A-2000-303925 has a limitation to increase the number of intake ducts or enlarge the cross-section area of the air intake ducts in a small or narrow engine compartment. Further, due to the pressure loss occurring when air is inhaled through the intake ducts, the intake air becomes insufficient when the engine operates at a high-speed high-load region. Thus, good engine performance is not achieved. When air is inhaled directly through the air intake opening of the air cleaner housing to avoid such a pressure loss caused by the intake duct, because the air warmed up in the engine compartment is inhaled, the thermal efficiency is decreased, and good engine performance is still not achieved.